As glazing substitutes, shatterproof or highly shatter resistant transparent materials have been widely utilized for these decades. For example, plastic substrates, especially polycarbonate resins have superior transparency, impact resistance and heat resistance and are currently used as structural members instead of glass in a variety of applications including building and vehicle windows and instrument covers.
The polycarbonate resins, however, are inferior to glass in surface properties such as mar resistance and weather resistance. It is desired to improve the surface properties of polycarbonate resin parts. Nowadays, polycarbonate resin parts for use as vehicle windows and acoustic barrier walls along highways are required to withstand more than 10 years of weathering.
Known means for improving the weather resistance of polycarbonate resin parts include the lamination of a weather resistant acrylic resin film on the surface of a polycarbonate resin substrate and the formation of a ultraviolet absorber-containing resin layer on the resin surface, for example, by co-extrusion.
For improving the mar resistance of polycarbonate resin parts, it is known to coat thermosetting resins such as polyorganosiloxanes and melamine resins and to coat photo-curable resins such as polyfunctional acrylic resins.
As to the manufacture of transparent articles having both weather resistance and mar resistance, JP-A 56-92059 and JP-A 1-149878 disclose ultraviolet-absorbing transparent substrates having a primer layer loaded with a large amount of UV absorber added and a protective coating of colloidal silica-containing polysiloxane paint overlying the primer layer.
However, several problems arise with this approach. The addition of a large amount of UV absorber can adversely affect the adhesion to the substrate. During heat curing step, the UV absorber can volatilize off. On outdoor use over a long period of time, the UV absorber will gradually bleed out, causing whitening. From the mar resistance standpoint, it is impossible to add a large amount of UV absorber to the protective coating of colloidal silica-containing polysiloxane.
From these considerations, it was also attempted to fix a UV absorber by silyl modification. For example, JP-A 57-21476 discloses alkylcarbamyl addition products of alkoxysilyl or alkanoylsilyl. Also U.S. Pat. Nos. 4,316,033 and 4,349,602 disclose silyl addition products obtained by reacting benzotriazole compounds with halogenated allyl compounds in the presence of bases. These methods, however, involve complex steps and are uneconomical.
Further, in JP-A 9-286912, the reaction product of a (meth)acrylic acid derivative of benzotriazole with an amino group-containing silane compound is added to a room temperature curable composition for the purpose of imparting weather resistance. In Japanese Patent Nos. 2,885,669, 2,885,671, and 2,885,672, a silyl-modified UV absorber in the form of a reaction product resulting from addition reaction between a benzotriazole containing a polymerizable vinyl group and a silane or silicone compound containing a Si—H group is used in cosmetic compositions as the sunscreen agent.
These silyl-modified UV absorbers are advantageous in that because of the inclusion of alkoxysilyl groups which undergo condensation reaction during the heat curing step, the absorbers are fixed within the coating during the heat curing step so that the absorbers might not bleed out. Heretofore, coating compositions having such silyl-modified UV absorbers added thereto and capable of forming mar and weather-resistant coatings have not been proposed.
It is also known from JP-A 6-299132, 7-90184 and 10-25434 that a copolymer of a benzotriazole based UV absorbing vinyl monomer or a benzophenone based UV absorbing vinyl monomer with another vinyl monomer copolymerizable therewith is used in tackifier compositions, light and chemical-resistant synthetic resins, and powder paint resins for the purpose of improving weather resistance. However, the use of such UV absorbing copolymers in a primer or undercoat layer is unknown. Undesirably, the use of such UV absorbing copolymers adversely affects the adhesion to the substrate and to the protective coating of colloidal silica-containing polysiloxane paint to be applied on the primer layer.
Moreover, it is known from JP-A 8-151415 that a mixture of a benzotriazole based UV absorbing vinyl monomer or a benzophenone based UV absorbing vinyl monomer and another vinyl monomer copolymerizable therewith is used in coating compositions which are effective for forming protective coatings on surfaces of synthetic resins. Since these protective coatings are based on vinyl polymers, their mar resistance is limited.